Exterior Door Jamb Installation

Back out the screws that hold the exterior door's hinges to the old jamb, using a drill with a Phillips driver bit. Remove the door from the opening. Back out all the screws that hold the jamb to the rough opening. There may be a few nails as well. Use a hammer or pry bar to pull the nails out. Push the old jamb out of the opening.

Run a thick bead of silicone caulk along the gap where the rough opening meets the siding, using a caulk gun. Do this on both sides of the opening and across the header -- the wooden board that runs over the opening. Run your finger over the caulk to smooth it.

Lift the new jamb's top two corners into the rough opening. Lower the two bottom corners to straighten the door in the opening. Drill a 1/8-inch pilot hole through the jamb's sides, about 3 inches from the top, using a 1/8-inch drill bit. Secure the jamb in place with a screw.

Go inside and check the gap between the jamb's header and the rough opening's header. If the gap is uneven, remove one of the screws and lift the jamb up to even out the gap, then replace the screw.

Hold a level to each jamb to ensure it is straight. Push wooden shims between the jamb and the rough opening if a gap exists. Place the wooden shims at the same height as the hinges. Drill a 1/8-inch pilot hole, behind the hinges; through the jamb, wooden shims and into the rough opening. Drive a screw through each pilot hole.

Drill out the 1/8-inch pilot holes if your home's siding is brick or stone, using a hammer drill. Secure the jamb in place with a masonry screw. Move to the handle-side jamb and drill 1/8-inch pilot holes through the jamb and into the rough opening. Place these screws at roughly the same height as the screws on the hinge jamb. Hang your door on the new jamb if you did not purchase a pre-hung exterior door.

Close the door and check the gap running between the door's edge and the jamb. If the gap is uneven, push wooden shims between the jamb and rough opening to push the jamb forward and narrow the gap. Adjust the wooden shims until the gap is even. Place these shims as close to the screws as possible for a tight fit.

Score the shims with a utility knife and bend them back and forth so they break off flush with the door jamb.